WASHINGTON (Reuters) - The U.S. Department of Agriculture's appeal to allow imports of Canadian cattle will be heard in Seattle on July 13, a clerk for the U.S. Court of Appeals Ninth Circuit in San Francisco told Reuters on Thursday.

The U.S. Agriculture Department is appealing a March ruling by a federal court in Montana that halted, at the request of U.S. ranchers group R-CALF USA, a government plan to allow imports of Canadian cattle under 30 months of age.

Some 67 consumer, food safety, agricultural and other groups urged the appeals court on Thursday to keep the U.S. border closed to Canadian cattle imports to protect the public health.

Supporters of R-CALF filed "friend of the court" documents, urging the appeals court to keep the border closed in the interest of public health.

A total of four cases of mad cow disease stemming from Canadian cattle have been identified since May 2003. Currently only Canadian beef from young slaughtered cattle -- which are believed to pose the least risk -- can be exported to the United States.

"The nation's human and bovine populations are jeopardized by baseless USDA action," the supporters said. Reopening the border to Canadian animals would mean "cattle from a diseased herd will come into the U.S., ending a ban designed to protect U.S. health interests," they said.

"If BSE (bovine spongiform encephalopathy) is vectored into this nation, thousands of cattle producers, millions of cattle, tens of millions of people and billions of dollars are at risk."

U.S. Agriculture Secretary Mike Johanns contends that Canada has sufficient safeguards in place to prevent the spread of mad cow disease. American meatpackers support the USDA, saying shipments of live cattle are urgently needed to avoid laying off workers and curtailing plant operations.

South Dakota rancher Ken Knuppe, participating in a media conference call to announce the latest filing, said allowing Canadian cattle imports into the United States could pose a significant risk to current negotiations with Japan. Japan, which once ranked as the biggest buyer of American beef with imports of $1.4 billion, is considering re-opening its market to U.S. imports.

"They don't want to be importing Canadian beef being sold as U.S. meat," Knuppe said, warning negotiations were likely to drag on if this was a worry.

Japan banned U.S. beef after the first American case of mad cow disease was discovered 17 months ago. The infected animal was a dairy cow in Washington state, which had been imported from Canada.

The final hearing in the Montana court is slated for July 27.

Both parties have 14 days to tell the San Francisco appeals court if the July 13 hearing date is acceptable.